Generally, semiconductor devices are used in a variety of electronic applications, such as computers, cellular phones, personal computing devices, and many other applications. Home, industrial, and automotive devices that in the past comprised only mechanical components now have electronic parts that require semiconductor devices, for example.
Semiconductor devices are manufactured by depositing many different types of material layers over a semiconductor workpiece or wafer, and patterning the various material layers using lithography. The material layers typically comprise thin films of conductive, semiconductive, and insulating materials that are patterned and etched to form integrated circuits (IC's). There may be a plurality of transistors, memory devices, switches, conductive lines, diodes, capacitors, logic circuits, and other electronic components formed on a single die or chip, for example.
Lithography involves transferring an image of a mask to a material layer of a wafer. The image is formed in a layer of photoresist, the photoresist is developed, and the photoresist is used as a mask during a process to alter the material layer, such as etching and patterning the material layer.
As feature sizes of semiconductor devices continue to decrease, as is the trend in the semiconductor industry, transferring patterns from a lithography mask to a material layer of a semiconductor device becomes more difficult, due to the effects of the light or energy used to expose the photoresist. A phenomenon referred to as the proximity effect results in the line width of patterns varying, depending the proximity of a feature to other features. Closely-spaced features tend to be smaller than widely-spaced features, although on a lithography mask they comprise the same dimension, as an example. It is important in many semiconductor device designs for features to have uniform, predictable dimensions across a surface of a wafer, for example, to achieve the required device performance.
To compensate for the proximity effect, optical proximity corrections (OPC) are often made to lithography masks, which may involve adjusting the widths or lengths of the lines on the mask. More advanced methods of OPC correct corner rounding and a general loss of fidelity in the shape of features by adding small secondary patterns referred to as serifs to the corners of patterns. The serifs, together with line width changes, enhance the amount of light transmitted through the transparent mask patterns.
The OPC design phase is time-consuming, and therefore costly. Often, it is desirable to introduce a product as quickly as possible to the market in the semiconductor device industry. However, it may take two or three weeks for OPC calculations to be performed on a semiconductor device design, for example.
Thus, what are needed in the art are faster and more efficient methods of calculating and determining OPC for lithography masks of semiconductor devices.